After that, Calibre has searched for ebook files in my tablet, and... the problem is it shows lots of files that I have stored in my tablet but they're not really ebooks.

For example, all downloaded articles by "Pocket" app (formerly "Read it latter" or "RIL") in my tablet are recognized as ebooks by Calibre. And I have quite a big amount of them! By the way, they are just HTML files, as far as I can see.

So, my question is this: Is there any way to tell Calibre to "scan" only some given folders in my tablet or to look only for .epub files, for example??